Briquetting of particulate materials has been carried out for many years. Typically, a material such as charcoal was compacted by briquetting apparatus at relatively low pressures and temperatures. In recent years, briquetting techniques have been applied to compact other materials, such as particulate metals or iron ores. Briquetting of such materials requires the use of high temperatures and pressures.
The use of high pressure between briquetting rolls and the maintenance of high pressure at elevated temperatures, as well as the abrasive nature of many materials, results in serious wear problems. Because of the serious wear problems encountered, briquetting press rolls having replaceable mold segments have received substantial commercial acceptance. Through the use of briquetting press roll designs employing replaceable mold segments, the severe wear problems encountered do not necessitate replacing an entire briquetting roll assembly, merely because the working surface has become worn.
Briquetting roll designs incorporating replaceable mold segments desirably possess a number of features. The design should permit the ready removal and replacement of worn segments. In addition, to retain proper alignment of mold cavities in cooperating rolls during briquetting operations, the mold segments should be rigidly retained in the press roll core so that they are constrained from moving relative to the core during briquetting operations. Furthermore, these desirable characteristics should be achieved in a design which is capable of being inexpensively fabricated without reliance upon extremely close tolerances.
A number of briquetting roll structures incorporating replaceable mold segments are known in the art. For various reasons, none of these is completely saatisfactory for use in present day briquetting operations.
One type of briquetting roll structure having replaceable mold segments is disclosed in U.S. Pat. No. 3,077,634. This briquetting roll comprises a cylindrical body adapted to receive a plurality of mold segments around the periphery of the cylindrical body, and at least two retaining rings which cooperate with the cylindrical body for maintaining the segments fixed to the cylindrical body. The mold segments of this design include two side walls which diverge with respect to each other relative to the bottom of the segment, and the retaining rings include inwardly beveled flanges adjacent their outer extremities which engage the converging end walls of the mold segments.
While this design has received some commercial acceptance, it is subject to several disadvantages. For example, to obtain rigid clamping of the mold segments in the cylindrical core, each of the segments must be precisely machined so that they are the same length. If one mold segment is longer than the others, it prevents the retaining rings from being drawn tightly about the other mold segments, and thus the other mold segments are free to move during briquetting operations.
If the segments are not tightly clamped in place, they tend to shift or rock in service and thereby destroy the cores. Moreover, in cases where the material being briquetted contains oil or some other liquid that lubricates the juncture between the segment and the clamping ring, this rocking of the segment becomes so severe that segmented rolls of this design cannot be used. This problem is aggravated by the fact that roll segments are always heat treated after machining and slight differences in the heat treating cycle or in the chemistry of the material will cause differences in the length of the segments and consequently significant differences in the rigidity with which they are clamped to the shaft.
In addition, the clamping action disclosed in U.S. Pat. No. 3,077,634 results from the axial translation of the circumferential retaining ring. For this reason, there is of necessity, axial clearance between the retaining rings and the roll core with the resultant consequence that there is no fixed axial position for the segments. Under this condition, sealing the two ends of the segments is difficult, or impossible. If the ends are not sealed, there will be leakage of particulate material past the sides of the rolls and satisfactory briquettes can not be formed.
The present invention overcomes many of the disadvantages of the present commercial briquetting apparatus, while providing a simple, easily maintained mold segment, retaining ring, and central core configuration applicable to most briquetting operations.
The invention also simplifies the structure and, hence the fabrication of the mold segment, the retaining means, and the central core of the briquetting roll. In addition, a mold segment structure is provided which is capable of being replaced without the need for extensive dismantling of the entire apparatus. Furthermore, the present invention provides a briquetting press roll in which clamping of replaceable segments in the roll core is achieved by translation of the clamping means toward the center of the core. Variations in the length of the segments do not affect the rigidity with which they are held.